Digital cameras operate by sampling light intensity information from a scene or subject and recording the light intensity information as a set of numerical values. Ideally, a digital camera produces output values that are a linear representation of the light intensity of the viewed scene. In a hypothetical ideal camera, a zero light intensity level would be recorded as a zero numerical value. However, real-world digital cameras have design limitations that prevent them from operating in this ideal manner.
A digital camera's dynamic range limits the ability of a digital camera to accurately record extreme high and low intensity values. For example, an 8-bit camera is limited to recording 256 possible intensity values for any one pixel. If the camera is used to record a scene with intensity values that exceed the highest intensity values that the camera is adapted to record, the recorded intensity values for the pixels corresponding to those high intensity values may not accurately reflect the true intensity. This effect is sometimes referred to as “saturation.” Analogously, if a scene has a very dark area that has intensity values that are lower than the lowest level of intensity that the camera is adapted to record, the recorded intensity values for the pixels corresponding to the low intensity area of the scene may not accurately reflect the true intensity. This effect is sometimes referred to as “undercut.” The limited dynamic range exhibited by digital cameras results in a loss of some intensity information at the high and low ends of the intensity spectrum. As a consequence, digital cameras sometimes do not accurately record areas of high and low brightness.
Digital cameras are sometimes susceptible to digitization errors. For example, because an 8-bit camera has only 256 possible intensity values with which it can record the intensity of a scene, an area of a scene with many fine variations in intensity may not be accurately reflected in the recorded pixel values. Rather, the intensity levels are approximated to one of the 256 intensity values, even if there are many more variations in the actual scene. Variations in intensity levels that cannot be recorded with an 8-bit level of detail may be lost.
Digital cameras may also be affected by noise. The gain experienced in a camera's electronics may result in inaccurate intensity level recordings. The effect of noise is often particularly noticeable in areas of low intensity such as dark or shadowed areas.
Digital cameras may not accurately record in the low intensity range due to black-level fluctuation. Black-level fluctuation may occur where different pixels in a camera's image sensor have different output values for zero intensity. Dark areas of a subject/scene with zero light intensity may be represented with different numerical values, depending on which pixels recorded the image. The lack of consistency in recorded intensity values may contribute to inaccurate representation of a scene.
Digital cameras that exhibit one or more limitations may be acceptable for use in many applications. For example, some level of inaccuracy may be acceptable where the camera is for use in amateur photography. However, for other applications such as, for example, machine vision applications, high levels of accuracy are often required. In some machine vision applications, such as polarization vision computations, it is preferred that a camera generate high levels of accuracy with respect to scene intensity levels.